Increasing numbers of individuals use marijuana in order to alleviate disease symptoms. The active component of marijuana, A9-tetrahydrocannabinol (THC), produces therapeutically beneficial effects such as analgesia, appetite stimulation, and nausea reduction, but also side effects including memory loss, and reduced motor coordination. THC mimics the action of the endocannabinoids anandamide (AEA) and 2- arachidonyl glycerol (2-AG). Unlike THC, administered AEA and 2AG have transient effects due to their prompt inactivation by fatty acid amide hydrolase (FAAH), monoacylglycerol lipase (MGL), and cyclooxygenase 2 (COX-2). Despite extensive study of in vitro endocannabinoid (eCB) metabolism, far less is known about the in vivo regional activity of MGL and FAAH in the brain. The overall goal of this proposal is to determine how FAAH and MGL contribute to eCB inactivation in the mouse brain by imaging in vivo [3H]AEA and [3H]2-AG metabolism on a regional and cellular level by autoradioagraphy. In Specific Aim 1, wild-type mice, and mice with FAAH genetically deleted, will be administered [3H]AEA and [3H]2-AG, their brains imaged, and compared to the regional FAAH, MGL, and COX-2 expression. In addition, circadian- and inhibitor-induced changes in endocannabinoid metabolism will be examined. Administered FAAH inhibitors produce a sub-set of cannabimimetic effects in rodents, such as analgesic and anxiolytic effects, while not affecting motor coordination. However, while inhibitors increase endocannabinoid tone, the exact mechanism producing this sub-set of behavioral effects remains elusive. In Specific Aim 2, [3H]AEA metabolism will be imaged in the presence of selective FAAH inhibitors. The regional inhibition of FAAH in brain and spinal regions will be compared to the behavioral effects induced by these compounds. These studies, the first to examine in vivo endocannabinoid metabolism, will give insight to the in vivo regulation of endocannabinoid tone, and the sites of action of FAAH inhibitors. These studies will provide valuable data for the development of medications alleviating symptoms such as pain and nausea without the psychotropic and addictive effects of marijuana use. The intensive neurobiology training will complement Dr. Glaser's biochemistry background and will enhance her career development by increasing her understanding of endocannabinoid metabolism and the scope of data interpretation in these studies.